1. Field of the Invention
The present invention relates generally to electronic circuits, and more specifically to an integrated circuit AND gate and related logic devices using either bipolar emitter coupled logic (ECL) or current mode logic (CML) devices, or both, implementing only a single low-voltage supply source for integration with CMOS logic circuits.
2. Description of the Prior Art
The ECL (emitter coupled logic) and CML (current mode logic circuits) are the fastest logic family in bipolar transistor technology. The operation of the bipolar CML and ECL digital gates is fast because they operate in a manner such as to avoid the saturation of their transistors. As shown in FIG. 1, there is illustrated a circuit diagram of a CML logic AND gate 10 having a stacked differential stage arrangement 12 according to the prior art. As known, CML logic implementing such stacked stage configurations require a comparably high supply voltage, typically above 3V in the latest technology.
For high-speed wired and wireless communication systems, high-speed ECL and CML circuits are integrated with high-density CMOS (complementary metal-oxide semiconductor) circuit in one chip. As CMOS transistors scale down for high-speed and high-integration, the supply voltage also scales down, but the bipolar circuits do not. This is because the supply voltage of the logic is high due to the stacked differential stages. Consequently, the system needs two supply voltage sources, one for bipolar circuit with high voltage, and the other for CMOS circuit with low voltage, which is not always desirable, especially for portable systems.
Razavi, as described in U.S. Pat. No. 5,289,055 and Razavi, et al. as described in the reference entitled xe2x80x9cDesign Techniques for Low-Voltage High-Speed Digital Bipolar Circuitsxe2x80x9d IEEE Journal of Solid-State Circuits, Vol. 29, No. 3, pp. 332-339, March 1994, has recognized use of bipolar ECL that avoids stacked differential stages for multiplexor, latch and XOR logic gates in low supply voltage applications, however, does not implement an AND function. G. Schuppener, et al. in the reference xe2x80x9cInvestigation on Low-Voltage, Low-Power Silicon Bipolar Design Topology for High-Speed Digital Circuitsxe2x80x9d IEEE Journal of Solid-State Circuits, Vol. 35, No. 7, pp. 1051-1054, July 2000, describes a CML frequency divider circuit with the circuit structure described in the Razavi references. The circuits described in Razavi and Schuppener, et al., however, do not require an AND logic gate.
It is the case that an AND gate is essential for all kinds of digital system designs, and also, low voltage systems, e.g., for portable applications.
It would thus be highly desirable to provide a low-supply voltage AND gate implemented for mix of bipolar-CMOS logic gates operable under one low-voltage supply source.
It would be further highly desirable to provide an ECL and CML logic AND gate that works under low supply voltage and preferably, that operates at voltages at or lower than the supply voltage used in for the latest CMOS technology.
It is an object of the present invention to provide a high-speed ECL and CML logic AND gate and related devices that operates under low supply voltages and preferably, operates at voltages at or lower than the supply voltage used in current CMOS technology.
It is a further object of the present invention to provide a high-speed ECL and CML logic AND gate and related logic devices operable with a single low-voltage power source and capable of integrating with CMOS logic devices for high-speed, low power electronic systems.
According to the invention, there is provided a single stack bipolar logic AND gate for low power applications comprising:
a first differential pair of transistors, each transistor of the first differential pair having base, emitter and collector terminals, a base of a first transistor of the first differential pair receiving an input signal A and a base of the second transistor of the first differential pair receiving its complementary signal {overscore (A)}, the emitters of each transistor of the first differential pair being connected at a common node to a first constant current source;
a second differential pair of transistors, each transistor of the second differential pair having base, emitter and collector terminals, a base of a first transistor of the second differential pair receiving an input signal B and a base of the second transistor of the second differential pair receiving its complementary signal {overscore (B)}, the emitters of each transistor of the second differential pair being connected at a common node to a second constant current source; and,
a common voltage power supply source,
the collector terminal of each first transistor of the first and second differential pairs being connected to the common voltage power supply source through a first resistance and defining a complement output node of the AND gate, and the collector terminal of each second transistor of the first and second differential pair being connected to the common voltage power supply source through a second resistance and additionally defining an output node of the AND gate, wherein the second resistance is greater than the first resistance.
Specifically, a single-stack AND gate of ECL and CML (current mode logic) systems is provided that may operate under very low supply voltage, e.g., as low as 1V supply. With this invention, the high-speed bipolar CML logic can be operated with low voltage CMOS logic circuits under the same low supply voltage.
Advantageously, the invention is suitable for high-speed front-end of wireless transceivers such as frequency synthesizer, especially the multi-modulus frequency divider, however may be implemented in many types of high frequency circuit applications, or, any ECL or CML system requiring low voltage applications.